'50 RCA KCS-47A Question

[7"estatdef]

Yup replaced the four 1000v jobs over by the damper and yoke socket. I won't get a chance to tinker till Monday but I've got lots of advice to try. I did check the brightness and it is the camera. The last pictures were in a fully lit room and the channel dial lite was on. You can't even see it in the pic. Stupid camera.
Tnx guys!
Terry

[kbmuri]

If you have a spare damper tube, swap it and look for changes. Rock the tube in the socket, maybe you've got a dirty contact there. I don't have your schematic, but typically you'll have a pair of .05uF capacitors straddling the horizontal linearity control. The 3 components are are collectively called the "boost network". The coil could be bad (unlikely) or the caps could be bad (more likely). If you've already replaced the caps, and you feel confident that they were good to begin with, doublecheck your solder joints and make sure the leads are short and proper.

[Tubejunke]

My TV Consultant 1955 Edition lists this as a "Barkhausen" oscillation. The cause is listed as "interference due to oscillations set up in the horizontal output tube and picked up by the tuner".

Possible fixes are interesting. One is listed as of course swapping tubes but the instuctions go on to say to try a specially designed anti-Barkhausen tube made by several tube manufacturers. I've never heard of these tubes. Also it says to reduce horizontal drive and check linearity adjustment.

Heres another neat idea. Probably the most interesting. Fasten a magnet such as an ion trap to the horizontal output tube and move it around until the line goes away.

Maybe my old book will help you! I hope so. The only other possibility I saw was yoke ringing which someone else mentioned.

[Eric H]

Barkhausen lines are much narrower and are usually a thin dark line instead of waves.

I found this illustration of Barkhausen:
http://books.google.com/books?id=ttB...G7PI#PPA225,M1

[kbmuri]

Barkhausen lines don't affect the sweep linearity either. Jordan has a genuine Barkhausen line here:



down the woman's right (stage-left) ear, down her jacket collar and between the 5 and 7 of the 576 phone exchange. It's very minor in his case so I didn't mention it, and it's not present in his other photos of the same set. As you can see, there's no squeezing or stretching of horizontal sweep around that line. Like Eric said, they're usually dark and thin. They also change with fine tuning and are more visible on weaker stations.

Damper failure lines don't change with tuning or signal strength, and affect linearity of the horizontal sweep. Keep looking around the damper-network circuit.

[7"estatdef]

I have another question. The two caps across the horiz linearity coil, are the values critical? Not on this set but others I've worked use a .035 cap which seems to be an odd value. Would a different cause a linearity issue? Like a .03 or .04 rather than the .035? Can a coil be bad if it isn't open? I'm thinking of my Admiral 20A1.
Terry

[Don Lindsly]

Ringing is usually caused by a mismatch. Note that the horizontal output transformer and yoke are in series, unlike most arrangements of the era. The lin coil, flyback and yoke must all match. Universal replacements for the flyback, yoke and lin coil rarely worked. Make sure you have RCA originals. The lin coil and surrounding components are critical. I discourage substitutes. When the lin coil is adjusted correctly, the width is at max and horizontal output tube current at minimum. That lin coil will have more effect than in conventional configurations.

If it has a green Merit HOT, you have probably found the problem.

Make sure the 500 mmf high voltage filter cap is OK.

Don

[Tubejunke]

Not trying to argue the point of Barkhausen lines but the books description of the video effect of this are as follows:

"Vertical dark faint line or lines on left side, followed by light area". I picked this out of the guide because it was closer to what I saw in the picture on this thread than the ringing symtoms/illustration. Actually I have never had trouble with either of these things. Just relaying information. Dont get me wrong, debate is great. All of our pool of knowledge here is an amazingly great thing. We are lucky to have AudioKarma!